scholarly journals Where is the western part of the Galactic Center Lobe located really?

2020 ◽  
Vol 72 (5) ◽  
Author(s):  
Masato Tsuboi ◽  
Takahiro Tsutsumi ◽  
Yoshimi Kitamura ◽  
Ryosuke Miyawaki ◽  
Atsushi Miyazaki ◽  
...  
Keyword(s):  
Galactic Center ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Low Frequency ◽  
Radio Observation ◽  
Galactic Latitude ◽  
Visual Extinction ◽  
Radio Recombination Line ◽  
Local Standard ◽  
H Ii Region

Abstract The Galactic Center Lobe (GCL) is a peculiar object widely protruding from the Galactic plane toward the positive Galactic latitude, which had been found toward the Galactic Center (GC) in the early days of the radio observation. The peculiar shape has suggested a relation with historical events, star burst, large explosion, and so on in the GC. However, the issue of whether the GCL is a single large structure located in the GC region is not yet settled conclusively. In the previous observations, the silhouette against the low-frequency emission was found in the western part of the GCL (WPGCL); this suggests that the part is located in front of the GC region. On the other hand, the Local Standard of Rest (LSR) velocity of the radio recombination line toward it was found to be as low as 0 km s−1. However, these observations cannot determine the exact position on the line-of-sight. There is still another possibility that it is in the near-side area of the GC region. In this analysis, we compare these results with the visual extinction map toward the GC. We found that the distribution of the visual extinction larger than 4 mag clearly corresponds to the silhouette of the WPGCL. The WPGCL must be located at most within a few kpc from us and not in the GC region. This would be a giant H ii region in the Galactic disk.

scholarly journals Remarkable Symmetries in the Milky Way Disc's Magnetic Field

2011 ◽  
Vol 28 (2) ◽  
pp. 171-176 ◽  
Author(s):  
P. P. Kronberg ◽  
K. J. Newton-McGee
Keyword(s):  
Magnetic Structure ◽  
Large Scale ◽  
Milky Way ◽  
Galactic Center ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Field Structure ◽  
Field Pattern ◽  
Close Coupling ◽  
Sign Change

AbstractWe apply a new, expanded compilation of extragalactic source Faraday rotation measures (RM) to investigate the broad underlying magnetic structure of the Galactic disk at latitudes ∣b∣ ≲15° over all longitudes l, where our total number of RMs is comparable to those in the combined Canadian Galactic Plane Survey (CGPS) at ∣b∣ < 4° and the Southern Galactic Plane (SGPS) ∣b∣<1.5°. We report newly revealed, remarkably coherent patterns of RM at ∣b∣≲15° from l∼270° to ∼90° and RM(l) features of unprecedented clarity that replicate in l with opposite sign on opposite sides of the Galactic center. They confirm a highly patterned bisymmetric field structure toward the inner disc, an axisymmetic pattern toward the outer disc, and a very close coupling between the CGPS/SGPS RMs at ∣b∣≲3° (‘mid-plane’) and our new RMs up to ∣b∣∼15° (‘near-plane’). Our analysis also shows the vertical height of the coherent component of the disc field above the Galactic disc's mid-plane—to be ∼1.5 kpc out to ∼6 kpc from the Sun. This identifies the approximate height of a transition layer to the halo field structure. We find no RM sign change across the plane within ∣b∣∼15° in any longitude range. The prevailing disc field pattern and its striking degree of large-scale ordering confirm that our side of the Milky Way has a very organized underlying magnetic structure, for which the inward spiral pitch angle is 5.5°±1° at all ∣b∣ up to ∼12° in the inner semicircle of Galactic longitudes. It decreases to ∼0° toward the anticentre.

scholarly journals The magnetic structure of our Galaxy: a review of observations

2008 ◽  
Vol 4 (S259) ◽  
pp. 455-466 ◽  
Author(s):  
JinLin Han
Keyword(s):  
Magnetic Fields ◽  
Magnetic Structure ◽  
Large Scale ◽  
Galactic Halo ◽  
Galactic Center ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Dust Emission ◽  
Measure Data ◽  
Radio Sources

AbstractThe magnetic structure in the Galactic disk, the Galactic center and the Galactic halo can be delineated more clearly than ever before. In the Galactic disk, the magnetic structure has been revealed by starlight polarization within 2 or 3 kpc of the Solar vicinity, by the distribution of the Zeeman splitting of OH masers in two or three nearby spiral arms, and by pulsar dispersion measures and rotation measures in nearly half of the disk. The polarized thermal dust emission of clouds at infrared, mm and submm wavelengths and the diffuse synchrotron emission are also related to the large-scale magnetic field in the disk. The rotation measures of extragalactic radio sources at low Galactic latitudes can be modeled by electron distributions and large-scale magnetic fields. The statistical properties of the magnetized interstellar medium at various scales have been studied using rotation measure data and polarization data. In the Galactic center, the non-thermal filaments indicate poloidal fields. There is no consensus on the field strength, maybe mG, maybe tens of μG. The polarized dust emission and much enhanced rotation measures of background radio sources are probably related to toroidal fields. In the Galactic halo, the antisymmetric RM sky reveals large-scale toroidal fields with reversed directions above and below the Galactic plane. Magnetic fields from all parts of our Galaxy are connected to form a global field structure. More observations are needed to explore the untouched regions and delineate how fields in different parts are connected.

scholarly journals Probing the structure of the Galactic disk through open clusters

2009 ◽  
Vol 5 (S266) ◽  
pp. 482-482
Author(s):  
Xiaoying Pang ◽  
Chenggang Shu
Keyword(s):  
Galactic Center ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Age Distribution ◽  
Outer Part ◽  
Simulation Models ◽  
Open Clusters ◽  
Galactocentric Distance ◽  
Distance Measurements ◽  
The Galaxy

AbstractThe WEBDA database of open clusters (hereafter OCs) in the Galaxy contains 970 OCs, of which 911 have age determinations, 920 have distance measurements, and 911 have color-excess data. Base on the statistical analysis of global properties of open clusters, we investigate disk properties such as the height above the Galactic plane. We find that old open clusters (age ≥ 1 Gyr) are preferentially located far from the Galactic plane with 〈|z|〉~394.5 pc. They lie in the outer part of the Galactic disk. The young open clusters are distributed in the Galactic plane almost symmetrically with respect to the Sun, with a scale height perpendicular to the Galactic plane of 50.5 pc. The age distribution of open clusters can be fit approximately with a two-component exponential decay function: one component has an age scale factor of 225.2 Myr, and the other consists of longer-lived clusters with an age scale of 1.8 Gyr, which are smaller than those derived by Janes & Phelps (1994) of 200 Myr and 4 Gyr for the young and old OCs, respectively. As a consequence of completeness effects, the observed radial distribution of OCs with respect to Galactocentric distance does not follow the expected exponential profile. Instead, it falls off both for regions external to the solar circle and more sharply towards the Galactic Center, which is probably due to giant molecular cloud disruption in the center. We simulate the effects of completeness, assuming that the observed distribution of the number of OCs with a given number of stars above the background is representative of the intrinsic distribution of OCs throughout the Galaxy. Two simulation models are considered, in which the intrinsic number of the observable stars are distributed (i) assuming the actual positions of the OCs in the sample, and (ii) random selection of OC positions. As a result, we derive completeness-corrected radial distributions which agree with an exponential disk throughout the observed Galactocentric distance in the range of 5–15 kpc, with scale lengths in the range of 1.6–2.8 kpc.

scholarly journals Study of a Far Infrared Cavity Around a Post-Asymptotic Giant Branch Star at Galactic Latitude -0.1º

2020 ◽  
Vol 6 (1) ◽  
pp. 97-104
Author(s):  
A. K. Gautam
Keyword(s):  
Galactic Plane ◽  
Far Infrared ◽  
Asymptotic Giant Branch ◽  
Color Temperature ◽  
Dust Particles ◽  
Galactic Latitude ◽  
Continuous Increase ◽  
Asymptotic Giant Branch Star ◽  
Planck Function ◽  
Visual Extinction

We present dust color temperature, Planck function and visual extinction distributions of a far infrared cavity FIC19+30 found to be located around post-AGB star namely AGB20+29 at the galactic plane. Minimum and maximum dust color temperature of the core region of the cavity was found to be (22.17±0.23) K and (22.41±0.29) K respectively with offset value 0.24 K which suggests that the cavity is isolated and stable. The product of dust color temperature and visual extinction was found to be in the order of 10-4 K mag. The distribution of Planck function along the extension (major diameter) and compression (minor diameter) was found to be non-uniform distribution. Specifically dust particles are oscillating in order to get dynamical equilibrium which may be the cause of grain temperature. It further suggests that the dust particles in the cavities might not be in the thermal equilibrium possibly due to pressure driven events of nearby AGB stars. There is continuous increase in flux density with increase in wavelength as in case of nebula which suggests that number density of dust particles increase according to the increase in wavelength and vice-versa.

scholarly journals Large scale magnetic fields of our Galaxy

2009 ◽  
Vol 5 (H15) ◽  
pp. 450-451
Author(s):  
JinLin Han
Keyword(s):  
Star Formation ◽  
Magnetic Fields ◽  
Large Scale ◽  
Galactic Halo ◽  
Galactic Center ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Zeeman Splitting ◽  
Radio Sources ◽  
Star Formation Regions

AbstractLarge-scale magnetic fields in the Galactic disk have been revealed by distributions of pulsar rotation measures (RMs) and Zeeman splitting data of masers in star formation regions, which have several reversals in arm and interarm regions. Magnetic fields in the Galactic halo are reflected by the antisymmetric sky distribution of RMs of extragalactic radio sources, which have azimuthal structure with reversed directions below and above the Galactic plane. Large-scale magnetic fields in the Galactic center probably have a poloidal and toroidal structure.

scholarly journals 8.1. Magnetic phenomena in galactic nuclei

1998 ◽  
Vol 184 ◽  
pp. 331-340 ◽  
Author(s):  
Mark Morris
Keyword(s):  
Magnetic Field ◽  
Galactic Center ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Galactic Nuclei ◽  
Relativistic Electrons ◽  
Predominant Orientation ◽  
The Right ◽  
The Magnetic Field ◽  
Intercloud Medium

The magnetic environment of the Galactic nucleus contrasts sharply with that of the Galactic disk. The inner few hundred parsecs of our Galaxy appear to be dominated by a strong (~milligauss) and uniform dipole field which dominates the pressure within the central intercloud medium. An attractive hypothesis for the origin of the central vertical field is that it results from the concentration of protogalactic field by radial inflow of gas throughout the Galaxy's lifetime. The predominant orientation of the magnetic field within dense molecular clouds is parallel to the galactic plane, which can be understood in terms of the strong tidal shear to which these clouds are subjected. The contrasting geometries of the cloud and intercloud fields allow for magnetic field line reconnection at cloud surfaces, which, under the right circumstances, could produce the relativistic electrons which delineate the nonthermal radio filaments near the Galactic center with their synchrotron emission. The characteristics of the Galactic center “magnetosphere” should be generalizable to all gas-rich spiral galaxies. Inadequate spatial resolution currently prevents us from exploring magnetic fields in other galactic nuclei to the same depth as in the Galactic center, but existing evidence is consistent with similar magnetic geometries elsewhere.

scholarly journals Interstellar Broadening of Compact Low Galactic Latitude Radio Sources

1984 ◽  
Vol 110 ◽  
pp. 309-312
Author(s):  
Brian Dennison ◽  
M. Thomas ◽  
J. J. Broderick ◽  
R. S. Booth ◽  
Robert L. Brown ◽  
...  
Keyword(s):  
Interstellar Medium ◽  
Radio Source ◽  
Electron Density ◽  
Galactic Center ◽  
Galactic Disk ◽  
Angular Diameter ◽  
Radio Sources ◽  
Galactic Latitude ◽  
Radio Waves

Scattering of radio waves off inhomogeneities in electron density in the interstellar medium can produce an apparent broadening in the angular diameter of an intrinsically compact background radio source. The magnitude and distribution of this effect at low galactic latitudes (|b|<5°) is not well known, although several cases suggest substantial broadening in certain directions, such as the Cygnus X region (Anderson et al. 1972), and the galactic center (Davies, Walsh, and Booth 1976). Large scattering in the plane is consistent with the scintillation properties of pulsars seen through substantial thicknesses (≳ 1 kpc) of the galactic disk.

scholarly journals A low-frequency view of mixed-morphology supernova remnant VRO 42.05.01, and its neighbourhood

2019 ◽  
Vol 622 ◽  
pp. A6 ◽  
Author(s):  
M. Arias ◽  
J. Vink ◽  
M. Iacobelli ◽  
V. Domček ◽  
M. Haverkorn ◽  
...  
Keyword(s):  
Spectral Index ◽  
Supernova Remnants ◽  
Galactic Plane ◽  
Low Frequency ◽  
Radio Spectrum ◽  
Optical Data ◽  
Shock Acceleration ◽  
H Ii Region ◽  
Radio Frequencies ◽  
Index Value

Context. Mixed-morphology supernova remnants (MM SNRs) are a mysterious class of objects that display thermal X-ray emission within their radio shell. They are an older class of SNRs, and as such are profoundly affected by the environment into which they evolve. VRO 42.05.01 is a MM SNR of puzzling morphology in the direction of the Galactic anticentre. Aims. Low-frequency radio observations of supernova remnants are sensitive to synchrotron electrons accelerated in the shock front. We aim to compare the low-frequency emission to higher frequency observations to understand the environmental and shock acceleration conditions that have given rise to the observed properties of this source. Methods. We present a LOFAR High Band Antenna map centred at 143 MHz of the region of the Galactic plane centred at l = 166 ° ,  b = 3.5° at 143 MHz, with a resolution of 148″ and an rms noise of 4.4 mJy bm−1. Our map is sensitive to scales as large as 6°. We compared the LOw Frequency ARay (LOFAR) observations to archival higher frequency radio, infrared, and optical data to study the emission properties of the source in different spectral regimes. We did this both for the SNR and for OA 184, an H II region within our field of view. Results. We find that the radio spectral index of VRO 42.05.01 increases at low radio frequencies; i.e. the LOFAR flux is higher than expected from the measured spectral index value at higher radio frequencies. This observed curvature in the low-frequency end of the radio spectrum occurs primarily in the brightest regions of the source, while the fainter regions present a roughly constant power-law behaviour between 143 MHz and 2695 MHz. We favour an explanation for this steepening whereby radiative shocks have high compression ratios and electrons of different energies probe different length scales across the shocks, therefore sampling regions of different compression ratios.

scholarly journals The Galactic center lobe filled with thermal plasma

2019 ◽  
Vol 71 (4) ◽  
Author(s):  
Halca Nagoshi ◽  
Yuzo Kubose ◽  
Kenta Fujisawa ◽  
Kazuo Sorai ◽  
Yoshinori Yonekura ◽  
...  
Keyword(s):  
Thermal Plasma ◽  
Galactic Center ◽  
Galactic Plane ◽  
Radio Continuum ◽  
Continuum Emission ◽  
Galactic Rotation ◽  
Observational Result ◽  
Recombination Line ◽  
The North ◽  
Radio Recombination Line

Abstract An observational result of a radio continuum and H92α radio recombination line of the Galactic center lobe (GCL), using the Yamaguchi 32 m radio telescope, is reported. The obtained spatial intensity distribution of the radio recombination line shows two distinctive ridge-like structures extending from the Galactic plane vertically to the north at the eastern and western sides of the Galactic center, which are connected to each other at a latitude of ${1{^{\circ}_{.}}2}$ to form a loop-like structure as a whole. This suggests that most of the radio continuum emission of the GCL is free–free emission, and that the GCL is filled with thermal plasma. The east ridge of the GCL observed with the radio recombination line separates 30 pc from the radio arc, which has been considered a part of the GCL, but coincides with a ridge of the radio continuum at a Galactic longitude of 0°. The radial velocity of the radio recombination line is found to be between −4 and +10 km s−1 across the GCL. This velocity is much smaller than expected from the Galactic rotation, and hence indicates that the GCL exists apart from the Galactic center. These characteristics of the GCL suggest that the long-standing hypothesis that the GCL was created by explosive activity in the Galactic center is unlikely, but favor that the GCL is a giant H ii region.

scholarly journals Radial abundance gradients in the outer Galactic disk as traced by main-sequence OB stars

2019 ◽  
Vol 625 ◽  
pp. A120 ◽  
Author(s):  
G. A. Bragança ◽  
S. Daflon ◽  
T. Lanz ◽  
K. Cunha ◽  
T. Bensby ◽  
...  
Keyword(s):  
Galaxy Evolution ◽  
Main Sequence ◽  
Galactic Center ◽  
Galactic Plane ◽  
Galactic Disk ◽  
Rotational Velocity ◽  
Solar Neighborhood ◽  
Elemental Abundance ◽  
Chemical Abundance ◽  
Ob Stars

Context. Elemental abundance gradients in galactic disks are important constraints for models of how spiral galaxies form and evolve. However, the abundance structure of the outer disk region of the Milky Way is poorly known, which hampers our understanding of the spiral galaxy that is closest to us and that can be studied in greatest detail. Young OB stars are good tracers of the present-day chemical abundance distribution of a stellar population and because of their high luminosities they can easily be observed at large distances, making them suitable to explore and map the abundance structure and gradients in the outer regions of the Galactic disk. Aims. Using a sample of 31 main-sequence OB stars located between galactocentric distances 8.4−15.6 kpc, we aim to probe the present-day radial abundance gradients of the Galactic disk. Methods. The analysis is based on high-resolution spectra obtained with the MIKE spectrograph on the Magellan Clay 6.5-m telescope on Las Campanas. We used a non-NLTE analysis in a self-consistent semi-automatic routine based on TLUSTY and SYNSPEC to determine atmospheric parameters and chemical abundances. Results. Stellar parameters (effective temperature, surface gravity, projected rotational velocity, microturbulence, and macroturbulence) and silicon and oxygen abundances are presented for 28 stars located beyond 9 kpc from the Galactic center plus three stars in the solar neighborhood. The stars of our sample are mostly on the main-sequence, with effective temperatures between 20 800−31 300 K, and surface gravities between 3.23−4.45 dex. The radial oxygen and silicon abundance gradients are negative and have slopes of −0.07 dex kpc−1 and −0.09 dex kpc−1, respectively, in the region 8.4 ≤ RG ≤ 15.6 kpc. Conclusions. The obtained gradients are compatible with the present-day oxygen and silicon abundances measured in the solar neighborhood and are consistent with radial metallicity gradients predicted by chemodynamical models of Galaxy Evolution for a subsample of young stars located close to the Galactic plane.

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